1. Field of the Invention
The present invention relates to a rotation control system, and more particularly it pertains to a system for stabilizing the rotation speed of a rotating body.
2. Description of the Prior Art
In a magnetic recording and reproducing device (hereinafter referred to as tape recorder) or like devices, the running speed of the tape mounted on the device should be kept precisely constant, and the rotation of a feed reel and a take-up reel should be stabilized or controlled for preventing the generation of wow-flutter and like phenomena. Various counter-measures have been proposed and employed for improving the characteristics of wow-flutter and like phenomena. Namely, from the mechanical and structural viewpoints, there have been employed means intended for making smooth the rotation of the pinch-roller and capstan and like parts for driving the tape, or for enhancing the accuracy of circularity of those rotating parts, or there has been provided a fly-wheel of large inertia and excellent balance attached to the capstan driving shaft, or there has been enhanced the processing accuracy of respective parts. Furthermore, from the electrical viewpoint, there have been adopted, for example, such counter-measures as that: a servo-motor is used for driving the tape, and that the running speed of a tape is detected electromagnetically or optically to control the servo-motor by the detection output, etc.
However, there are limitations in successfully achieving the above-mentioned improvements in the mechanical aspects, and the use of a servo-motor in the electrical aspects inevitably brings about a substantial increase in the manufacturing cost since the servo-motor is expensive. Therefore, such counter-measures have been employed only in high grade systems for use in, for example, broadcasting stations. From the economical viewpoint, therefore, none of the conventionally proposed counter-measures can be employed as desirable improvements. Furthermore, these conventional counter-measures have been proposed mainly for the purpose of stabilizing the fluctuations in the rotation of the rotating members of the capstan system. Regarding the driving of the tape reels, only a weak driving force has been given to the reel through a slipping driving mechanism or a braking mechanism so as to prevent the occurrence of slackening of the tape during running.
In such conventional devices, fluctuations or variation of the tape running speed are unavoidable due to various causes, such as the variations in the tension of the tape, which tension changing depending on the amount of the tape wound around a tape reel and the variations in the rotating torque acting on the tape reel by the running tape, and deviations of the thickness and also depending on the friction of the tape itself. However, adequate and effective means never has been proposed in the past for easily and economically satisfying the general requirements for ensuring high fidelity operation in various kinds of magnetic recording and reproducing devices.